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Subsystem Attachment Package

IP.com Disclosure Number: IPCOM000045133D
Original Publication Date: 1983-Feb-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 6 page(s) / 24K

Publishing Venue

IBM

Related People

Ojala, RN: AUTHOR [+3]

Abstract

This article describes a method for operating a computing apparatus to provide communication between a subsystem instance and an application program executing in at least one dependent region under control of an information management system control region instance.

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Subsystem Attachment Package

This article describes a method for operating a computing apparatus to provide communication between a subsystem instance and an application program executing in at least one dependent region under control of an information management system control region instance.

In accordance with the method, subsystem provided exits are executed to establish a communication connection (thread) from the control memory to the subsystem instance and from the dependent region to the subsystem instance. The execution of the exits occurs selectively during initialization processing of a message region processor (MPP) or upon issuance of a first subsystem request (SQL request) from a batch message region processor (BMP) to the subsystem instance. Responsive to a subsystem request directed by the application to the subsystem instance while a thread connection is present from the application to the subsystem, a subsystem request (NORMAL CALL EXIT) is communicated to the subsystem instance for execution and for returning the response to the application. The subsystem provided exits are stored in an external subsystem module table in a subsystem library data set or, alternatively, in a data set (DFSESL) provided by the information management subsystem instance, and are accessed by a pointer from a member in a procedure library (PROCLIB) maintained in main memory.

The procedure library (PROCLIB) member further includes a region error option (REO) parameter specifying the action to be taken by the information management system instance in the event that an application service request is issued before the communication connection is completed or upon failure of the connection before the service request is answered. The action to be taken is selectively specifiable as () issuing a return code to the application, (2) enqueuing the application request for subsequent execution when the connection is established, or (3) abending the application.

The Subsystem Attachment Package of this article may be used as a mechanism (bridge) that permits user application programs and an information management system (such as IBM's IMS/VS Version 1) to access resources (e.g., data bases) owned and managed by other subsystems.

IMS/VS, for example, requires the external subsystem to supply exits (i.e., modules) that can reside in the supported IMS/VS memories (Control - Message Processing (MPP) ; Batch Message Processing (BMP); Fast Path (IFP)). Each exit has a defined function to perform in the establishment of the connection from IMS/VS to the external subsystem for that memory. A defined subsystem interface protocol dictates the order in which the exits are invoked and the function they must perform.

EXIT DEFINITION - In order to load and subsequently invoke the exits they must first be defined to IMS/VS via an External Subsystem Module Table (ESMT). The ESMT is supplied by the external subsystem and contains the names of the modules as they res...